Dragline excavator
The largest walking dragline produced as of 2014 was Joy Global’s digital AC drive control P&H 9020XPC, which has a bucket capacity of 110–160 cu yd (84–122 m3) and boom lengths ranging from 325–425 ft (99–130 m); working weights vary between 7,539 and 8,002 tons.
[1] Draglines fall into two broad categories: those that are based on standard, lifting cranes, and the heavy units which have to be built on-site.
These units (like other cranes) are designed to be temporarily dismantled and transported over the road on flatbed trailers.
The much larger type which is erected on site is commonly used in strip-mining operations to remove overburden above coal and more recently for oil sands mining.
The hoist rope, powered by large diesel or electric motors, supports the bucket and hoist-coupler assembly from the boom.
In 1907, Monighan's Machine Works of Chicago became interested in manufacturing draglines when local contractor John W. Page placed an order for hoisting machinery to install one.
In 1913, a Monighan engineer named Oscar Martinson invented the first walking mechanism for a dragline.
Bucyrus purchased a controlling interest and the joint company became known as Bucyrus-Monighan until the formal merger in 1946.
After WWI, demand for excavators increased and in 1924 they reached an agreement to build Marion draglines from 1 to 8 cubic yards capacity.
The Marion Power Shovel Company (established in 1880) built its first walking dragline with a simple single-crank mechanism in 1939.
In 1912 Bucyrus helped pioneer the use of electricity as a power source for large stripping shovels and draglines used in mining.
Bucyrus' largest dragline was Big Muskie built for the Ohio Coal Company in 1969.
Heavy Engineering Corporation Limited was the first Indian company to manufacture a walking dragline of 31-yard bucket capacity.
On smaller draglines, a skilled operator could make the bucket land about one-half the length of the jib further away than if it had just been dropped.
A large dragline system used in the open pit mining industry costs approximately US$50–100 million.
Their power consumption on order of several megawatts is so great[quantify] that they have a direct connection to the high-voltage grid at voltages of between 6.6 and 22 kV.
A typical[further explanation needed] dragline weighing 4000 to 6000 tons, with a 55-cubic-metre bucket, can use up to 6 megawatts during normal digging operations.
Because of this, many (possibly apocryphal) stories[example needed] have been told about the blackout-causing effects of mining draglines.
But mining draglines due to their reach can work a large area from one position and do not need to constantly move along the face like smaller machines.
While a dragline can dig above itself, it does so inefficiently and is not suitable to load piled up material (as a rope shovel or wheel loader can).
The coal mining dragline known as Big Muskie, owned by the Central Ohio Coal Company (a division of American Electric Power), was the world's largest mobile earth-moving machine, weighing 13,500 tons and standing nearly 22 stories tall.
[15] It operated in Muskingum County, in the U.S. state of Ohio from 1969 to 1991, and derived power from a 13,800 volt electrical supply.
The British firm of Ransomes & Rapier produced a few diesel-electric excavators rather over 1/10th its size, the largest in Europe in the 1960s at 1400-1800 tons.
After its working life at the first site in Rutland wrapped it walked 13 miles (21 km) in 9 weeks to Corby, where it continued on till being scrapped from January to June 1987.
The basic mechanical technology of draglines, unlike that of most equipment used in earth-moving, has remained relatively unchanged in design and control functions for almost 100 years.
Some advances, however, have been made (such as hydraulic, then electro-hydraulic, controls (including joysticks) and using simulation software to train new operators), are being pursued (such as improved automation systems), or are arguable as a step forward (as is "universal dig-dump" (UDD)): Researchers at CSIRO in Australia have a long-term research project[16] into automating draglines.
UDD machines generally have higher productivity than a standard dragline, but often have greater mechanical issues.
